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Robots and radios. A pair made in robot heaven. I’m always on the beat
looking for new and unique stuff to use in the real world. When I find
something that’s truly useful and it really works, it ends up filtering out
through my fingers onto the printed page.

The editorial goo that formed this month’s discussion is provided by RF Digital.
Our discussion will revolve around a radio module that can act as an RFID
device, a key fob, and a wireless serial link. All we have to do is choose the
mode of operation and flip the power button.

The RF Digital RFD21733

The tiny radio module I’ve captured in Photo 1 is an
out-of-the-box ready to use fully FCC compliant 2. 4 GHz
transceiver. This particular radio is designed to be highly
tolerant to noise and other 2. 4 GHz interference. In that
the RFD21733 can operate in noisy motor environments
and fend off 2. 4 GHz Wi-Fi traffic, it is perfectly suited to

52 SERVO 06.2012

robotic applications. The robust operation of the
RFD21733 is attributed to the built-in RFDP8 interference-tolerant user application protocol. RFDP8 is inherent to the
RFD21733 and transparent to the user.

The RFD21733 can be coaxed into RFID mode (Mode
0), Logic Switch Transmitter/Receiver mode (Modes 1, 4,
5, 6, 7), or act as a 9600-8N1 Serial UART Transceiver
(Mode 2, 3). If that’s not enough, the RFD21733 is
network capable, as well. Modes 3, 5, and 7 are the
network mode variants. To support the various network
modes, a unique 32-bit ESN (Electronic Serial Number) is
assigned to every RFD21733.

The kicker is that we don’t need a microcontroller or
complex firmware to get to all of that functionality. It’s all
available with the push of a button. Our RFD21733 radio
module is actually mounted on an RF Digital RFD21737
evaluation board. All of the pushbuttons, DIP switches,
LEDs, and logic we need to put the RFD unit through its
paces are packed on the evaluation board. The entire
evaluation board complete with an RFD21733 transceiver
is shown in Photo 2.

The evaluation board includes a three-position DIP
switch that is used to select the RFD21733’s mode of
operation. There are three pushbuttons that allow their
logic levels to be transmitted in three-Input Switch Logic
Transmitter mode (Mode 1). Each pushbutton is
complemented by an LED that displays the transmitted

PHOTO 1. The RFD21733 is a complete radio transceiver
subsystem and includes an on-module antenna.